1. Field of the Invention
The present invention relates to easy-open ends for product containers, particularly, beverage and beer cans. In particular, the present invention provides an improved method for forming easy-open ends, improved tooling, and an improved can end that demonstrates superior functionality, particularly in its opening characteristics.
2. Prior Art
Many metallic cans for holding beverages or other products are provided with easy-open can ends, wherein a pull tab attached to a tear strip that is defined by a score in the can end. The pull tab may be lifted and then pulled to provide an opening in the can end for dispensing the can's contents. For ecological and safety reasons, many regions require that the tear strip and attached pull tab be retained to the can end after opening. In order to meet these requirements, various designs have been suggested by the prior art for ensuring that the tear strip and pull tab do not become separated from the can end. Generally, the pull tab is retained on the can end by means of a rivet. Methods of forming a can end can be found in U.S. Pat. Nos. 4,465,204 and 4,530,631 both to Kaminski et al., and assigned to the assignee of the instant invention. These patents are incorporated by reference as if fully set forth herein.
In the manufacture of an easy-open can end, a can end shell is first formed from a metal sheet product, preferably an aluminum sheet product. The can end shell is then transferred to a conversion press. In the typical operation of a conversion press, a can end shell is introduced between an upper tool member and a lower tool member which are in the open, spaced apart position. A press ram advances the upper tool member toward the lower tool member in order to perform any of a variety of metal forming operations such as rivet forming, paneling, scoring, embossing, tab securing, and final staking. After performing an operation, the press ram retracts until the upper tool member and lower tool member are once again in the open, spaced apart position. The partially converted shell is transported to the next successive tooling operation until an easy-open can end is completely formed and discharged from the press. As one shell leaves a given tooling operation, another shell is introduced to the vacated operation, thus continuously repeating the entire easy-open can end manufacturing process.
In certain canned products, such as carbonated beverages, there is substantial internal pressure that can be in the order of 90 to 100 psi or even greater, and must be quickly and safely vented during the initial opening of the can end by the consumer. According, can ends are constructed for venting or releasing the internal pressure of the container during the initial operation of the easy open mechanism of the end. The mechanism of venting is described in prior art patents such as U.S. Pat. Nos. 4,015,744 and 4,030,631, the contents of which are incorporated by reference herein as if fully set forth. As briefly mentioned above, the easy open mechanism includes an end panel which is attached to the can body or container. A tear panel is defined in the end panel by a scoreline. An operating tab including a nose which extends partially over the tear panel is connected by a rivet to the end panel. The rivet defines a pivot point for tab operation. My co-pending patent application U.S. Ser. No. 08/476,406, filed Jun. 7, 1996, entitled, "Improved Easy Open Container End, Method of Manufacture, and Tooling" discloses new features that cooperates with the scoreline.
Basically, initial lifting of the tab produces an upward force on the rivet and a downward force on the edge of the tear panel adjacent a beginning point of the tear panel scoreline. This in turn causes an initial opening of the tear panel beneath the nose of the tab in an area referred to as the vent region of the can end. Further lifting motion of the tab causes the tear panel to separate progressively along its scoreline, leaving a small integral connection or hinge between the end panel and the tear panel, about which the tear panel is rotated. The separation of the tear panel defines an opening through which container's contents can be poured.
As mentioned above, there can be substantial internal gas pressure in the container. During the initial opening motion, this gas pressure must vent safely. It is the typical practice to define a small vent opening with a hook formation at the radially inward end of the scoreline. The vent opening or region extends to a score stop located in the region where the tear panel scoreline proceeds outward at the end. Typically, the score stop is in the form of a shallower segment of the scoreline of relatively short length as described in U.S. Pat. No. 4,503,989. The contents of this patent are incorporated herein by reference as if fully set forth. This score stop provides an increase in tear resistance along the scoreline. This opening process can be identified by the initial "pop" that is heard when the tab is lifted, followed by the "metal tearing" sound that accompanies the separation of the tear panel from the can end as the nose of the tab is "pushed" against the tear panel.
The continuing evolution toward larger tear away panel opening areas relative to the overall surface area of the can end has created several challenges in the can making industry. This relative size of the tear away panel is at least in part the result of the continuous down-sizing of can end diameters.
It is useful to understand what is meant by reference to a "large" opening end or to "larger" tear away panels. For example, a conventional 202 easy open end has a tear away panel that defines an area of approximately 0.450 square inches. The same 202 easy open end that is equipped with a larger tear away panel has a panel that defines an area of approximately 0.596 square inches. Accordingly, a large opening end may be characterized as being between about 20% and 40% larger than a conventional tear panel. Among the challenges associated with larger tear away panels are: the prevention of missiling or tear panel blow off, i.e., the catastrophic failure of the tear panel; the efficient mechanical operation of the larger tear panel with the use of the existing tab; the avoidance of the partial opening or incomplete opening of the tear panel; and maintaining "pop" and "push" values at a level that is satisfactory and convenient to the end user. Examples of large opening ends are available in my co pending patent applications, including application Ser. No. 29/048,638.
The instant invention also addresses a technique for providing heightened control of the panel opening process through the use of a tab nose bead formed into the tear away panel.
It is an object of this invention to provide a can end having a large opening tear panel that demonstrates improved and consistently-acceptable operational capabilities.
It is yet another object of this invention to provide a can end tear away panel configuration suitable for use with both conventional and large opening ends.
It is still another object of this invention to provide an improved set of tooling for the manufacture of converted can ends.
It is another object of this invention to provide a converted can end and a method for manufacturing the same.